Journey to the Typhoon

Application of UAVs (unmanned aerial vehicles) for tropical cyclone missions is an emerging area of research and recent advances include the concept of spinsonde for multi-cycle measurement of vertical wind profile within the storm. This work proposes the design of a typhoon UAV as part of a cost-effective approach for acquiring atmospheric data to improve prediction and refine models. Land- and carrier-based flight schemes are proposed in this study and computer simulations are carried out to investigate the flight performance. Results suggest that the UAV achieves a maximum cruising speed in excess of 350 km·h-1 with excellent spinsonde performance. Furthermore, the UAV is capable of performing high-alpha maneuvers as well as vertical landing, thus rendering it suitable for space-efficient operation whether on land or aircraft carrier.

PTVC-M for Ultra-Agile VTOL and 300+ km·h-1 Cruising

There remains a need to develop improved VTOL techniques that are cost-effective and with minimum compromise on cruising flight performance for fixed-wing aircraft. This work proposes an elegant VTOL control method known as PTVC-M (pitch-axis thrust vector control with moment arms) for tailsitters. The hallmark of the approach is the complete elimination of control surfaces such as elevators and rudder. Computer simulations with a 1580 mm wing span airplane reveal that the proposed technique results in authoritative control and unique maneuverability such as inverted vertical hover and stall-spin with positive climb rate. Zero-surface requirement of the PTVC-M virtually eliminates performance tradeoffs between VTOL and high-speed flight. In this proof-of-concept study, the VTOL-capable aircraft achieves a VH of 360 km·h-1 at near sea-level. The proposed technique will benefit a broad range of applications including high-performance spinsonde that can directly measure 10-m surface wind, tropical cyclone research, and possibly serving as the cornerstone for the next-generation sport aerobatics.

Retarded Harrier Maneuver as a New and Efficient Approach for Fixed-Wing Aircraft to Achieve S/VTOL

Modern day VTOL fixed-wing aircraft based on quadplane design is relatively simple and reliable due to lack of complex mechanical components compared to tilt-wings or tilt-rotors in the pre-80’s era. Radio-controlled aerobatic airplanes have thrust-to-weight ratio of greater than unity and are capable of performing a range of impressive maneuvers including the so-called harrier maneuver. We hereby present a new maneuver known as the retarded harrier that is applicable to un/manned fixed-wing aircraft for achieving VTOL flight with a better forward flight performance than a quadplane in terms of weight, speed and esthetics. An airplane with tandem roto-stabilizers is also presented as an efficient airframe to achieve VTOL via retarded harrier maneuver, and detailed analysis is given for hovering at 45° and 60° and comparison is made against the widely adopted quadplane. This work also includes experimental demonstration of retarded harrier maneuver using a small remotely pilot airplane of wingspan 650 mm.

Density Functional Based Tight Binding (DFTB) Study on the Thermal Evolution of Amorphous Carbon

Density functional based tight binding (DFTB) model is employed to study the sp3-to-sp2 transformation of diamond-like carbon at elevated temperatures. The understanding could lead to the direct-growth of graphene on a wide variety of substrates.

Radio Controlled “3D Aerobatic Airplanes” as Basis for Fixed-Wing UAVs with VTOL Capability

There are fundamental performance compromises between rotary-wing and fixed-wing UAVs. The general solution to address this well-known problem is the design of a platform with some degree of reconfigurable airframes. For critical missions (civilian or military), it is imperative that mechanical complexity is kept to a minimum to help achieve mission success. This work proposes that the tried-and-true radio controlled (RC) aerobatic airplanes can be implemented as basis for fixed-wing UAVs having both speed and vertical takeoff and landing (VTOL) capabilities. These powerful and highly maneuverable airplanes have non-rotatable nacelles, yet capable of deep stall maneuvers. The power requirements for VTOL and level flight of an aerobatic RC airplane are evaluated and they are compared to those of a RC helicopter of similar flying weight. This work provides quantitative validation that commercially available RC aerobatic airplanes can serve as platform to build VTOL capable fixed-wing UAVs that are agile, cost effective, reliable and easy maintenance.

Roto-Stabilizer for Superb Pitch-Related Post-Stall Maneuvers and STOL

Stabilizers and their control surfaces are vital components in maneuvering an airplane during flight. However, a shortcoming of stabilizers is that they require airstream or propeller wash for them to work properly. In this work, we propose the concept of roto-stabilizer as viable substitution for conventional horizontal stabilizer. A key benefit of the proposed technique is its ability to exert powerful moment in the absence of forward airspeed or propeller wash. Proof of principle is demonstrated via computer simulations. Results reveal that new aerobatic maneuvers are made possible. Furthermore, when implemented in canard configuration, it is possible to achieve ultra-STOL and VTOL.

Concept of Spinsonde for Multi-Cycle Measurement of Vertical Wind Profile of Tropical Cyclones

Tropical cyclones and cyclogenesis are active areas of research. Chute-operated dropsondes are capable of acquiring high resolution vertical wind profile of tropical cyclones. This work proposes a chute-free vertical retardation technique (termed as spinsonde) that can accurately measure vertical wind speed profile. Unlike the expendable dropsondes, the spinsonde allows multi-cycle measurement to be performed within a single flight. Proof of principle is demonstrated via simulation and results indicate that the ground speed correlates with the wind speeds to within ±5 km·h-1. This technique reduces flying weight and increases payload capacity by eliminating bulky chutes. Maximum cruising speed (VH) achieved by the spinsonde UAV is 368 km·h-1.

Isopropanol as Fuel for Small Unmanned Aircraft

Gasoline engines are increasingly popular for use in small unmanned aircraft requiring endurance due to the specific energy of gasoline (47.3 MJ·kg-1) and its cost effectiveness. However, gasoline is volatile and it poses a health hazard. In this work, isopropanol is proposed and investigated as viable fuel for small gasoline engines. Isooctane is used as a benchmark for performance comparison. The field testing reveals that isopropanol offers similar running performance and ease of starting. The maximum output power of isopropanol is surprisingly found to occur at a more advanced ignition timing compared with isooctane. The significant outcome of this study is that isopropanol can readily be used as a replacement fuel for existing engines without the need for any modifications to the ignition module or the engine itself.

Rotosonde: Acquiring Vertical Wind Profile of a Tropical Cyclone with Small Unmanned Helicopters

Spinsonde is a chute-free vertical retardation technique specifically developed for fixed-wing unmanned aircraft to acquire accurate measurement of vertical wind speed profile for meteorological applications. Key advantages of spinsonde over the expendable chute-operated dropsondes are the ability to acquire multi-cycle measurement, efficient use of payload capacity and cost-effectiveness. This work proposes the concept of “rotosonde”, which is the spinsonde equivalent for unmanned helicopters. Computer simulations are carried out to evaluate the performance of the rotosonde and results indicate that the measured speed generally correlates with the wind speed to within ±3 km·h﹣1 even for intensities in excess of 180 km·h﹣1. The profound implication of this work is that unmanned helicopters can now be considered for important field of studies such as cyclogenesis given their reliability to operate in gusty wind conditions in remote oceans, particularly during docking and launching from carriers.